Database Management Systems
In MySQL, the CASE operator compares a list of conditions and returns one of multiple possible result expressions.
The CASE expression is included in the SQL standard (ISO/IEC 9075), and most major RDBMSs support it.
MySQL also has the CASE statement, which is slightly different to the CASE operator. This article is about the CASE operator.
Here are four options for returning rows that contain lowercase characters in PostgreSQL.
Continue readingIn MariaDB, we can use the CASE operator to compare a list of conditions and return a different result depending on which condition (if any) is matched.
The CASE expression is included in the SQL standard (ISO/IEC 9075), and most major RDBMSs support it.
MariaDB also has the CASE statement, which is slightly different to the CASE operator. This article is about the CASE operator.
Below are examples of using some of the more popular RDBMSs to return the Unix timestamp.
The Unix timestamp (also known as Unix Epoch time, Unix time, or POSIX time) is the number of seconds that have elapsed since 00:00:00 Thursday, 1 January 1970, Coordinated Universal Time (UTC).
Continue readingHere are two options for returning the number of days in a given month in SQLite. This could be the number of days in the current month, or it could be based on a given date.
Continue readingSome RDBMSs provide an IFNULL() function that can be used when dealing with potentially null values. In particular, MySQL, MariaDB, and SQLite each have an IFNULL() function that replaces any null values with another value.
Other RDBMSs, such as SQL Server, Oracle, and PostgreSQL provide similar functionality via functions of a different name.
Continue readingIn MariaDB, the ISNULL() function checks whether an expression is null or not. If the expression resolves to null, then ISNULL() returns 1, otherwise it returns 0.
If you ever encounter a character column that should be numeric, there’s always a possibility that it contains non-numeric data that you don’t know about.
For example, someone might have set up a Price column as a varchar column that should have been a numeric column, and now you need to clean up after them. You might start by identifying all non-numeric data so that you can work out what to do with it before converting the column to a numeric type.
In SQL, you can run a query to return non-numeric data from the column. The query you use will largely depend on your DBMS.
Continue readingIf you have a column in a database table that contains character data, but some rows also contain numbers, you can use the following SQL queries to return just those rows that don’t contain numbers within the value.
Continue readingIn SQL, the CASE statement evaluates a list of conditions and returns one of multiple possible result expressions.
In some ways, the SQL CASE statement is kind of similar to the IF...ELSE statement in that it allows us to check for a given condition and return a different result depending on the outcome.